The invention relates to a planetary gear and in particular to a thrust washer of a planetary gear. In transmissions, such as planetary gears, it is standard practice to dispose thrust washers at each planetary wheel, the thrust washers ensuring the correct support of the planetary wheels and the function of the transmission when subject to outside influences. EP1099882B1 thus describes the use of an elastic thrust washer between each planetary wheel and the planetary carrier, the thrust washer absorbing the axial thrust of a planetary wheel and also being deformable in its elastic region, to the extent that, even should the planetary carrier be deformed, the bearings of the planetary wheels have a uniform load and vibrations in the planetary gear are dampened.
EP1686290A1 and EP1580459A2 describe thrust washers that are likewise seated between each planetary wheel and the planetary carrier and that engage in corresponding recesses in the planetary carrier using fixing elements on the thrust washer taking the form of nubs or lugs, so that their exact position within the planetary gear is safeguarded even when subject to heavy loads.
A planetary gear made by IMS Gear GmbH Donaueschingen (DE) is known in which a thrust washer is inserted between the planetary wheels and the drive motor to prevent the planetary wheels from coming into contact with the motor flange during rotation. In contrast to the above-mentioned thrust washers, this thrust washer covers all planetary wheels of the planetary carrier of a first gear stage. The rotation of the planetary wheels produces a relative movement between the adjacent thrust washer and the annulus gear. A gear design is known in which this relative movement is prevented by bonding the thrust washer fixedly to the annulus gear.
If the thrust washer is not fixed or bonded, the rotation of the planetary wheels results in a movement of the thrust washer with respect to the annulus gear. Depending on the material of the annulus gear, the movement of the thrust washer may result in the thrust washer cutting into the toothed rim of the annulus gear. This produces wear that becomes established in the gearing and leads to premature failure of the transmission.
The same problem is found in those thrust washers that are disposed in multistage planetary gears between the individual gear stages and which protect the planetary wheels of one gear stage against the planetary carrier of an adjacent gear stage. If the thrust washer is not firmly fixed, the problem again arises here of the thrust washer cutting into one of the gear parts.
Although bonding the thrust washer may solve the above-mentioned problem, it represents extra work and expense in terms of process engineering. The process of bonding a thrust washer involves cleaning the bonded surfaces, the precise mechanical application of a defined amount of adhesive and the setting of the adhesive. Not only does this require additional materials, it also means that the manufacturing cycle is greatly prolonged.